Sheindorf Rebuhn Sheintuch Research Articles

Ofloxacin and doxycycline competitive/binary adsorption on to MCM-41: isotherm modelling and evaluation

ABSTRACT This work investigates the competitive adsorption of ofloxacin (OXC) and doxycycline (DCL) form OXC-DCL binary solution on to MCM-41, not reported earlier. Experiments were conducted at 288–318 K temperatures, and equilibrium adsorption isotherm data were analysed to study the competitive effect of the presence and absence of DCL on OXC adsorption and vice-versa in OXC-DCL binary solution. On this basis, the competitive interaction, Synergistic, Antagonistic and No interaction effects, for OXC and DCL adsorption was evaluated. Furthermore, the experimental equilibrium adsorption data were used for isotherm modelling using various multi-component competitive isotherm models such as extended Langmuir, extended Freundlich and Sheindorf–Rebuhn–Sheintuch (SRS) isotherms. It was found that single component adsorption for OXC, and OXC adsorption in the presence of DCL and vice-versa followed Freundlich and extended Freundlich isotherm model, respectively. The competitive adsorption interaction between OXC and DCL from their binary solution was found to be antagonistic at all temperatures.

Modelling of chromatographic carboxylic acid fractionation with a strong anion exchange resin in sulfate form

Chromatographic fractionation of complex mixtures of carboxylic acids with a strong anion exchange resin in sulfate form as separation material was modelled. The studied system contained lactones of two isosaccharinic acids, four dissociating monocarboxylic acids (lactic acid, glycolic acid, acetic acid, and formic acid), and two strong electrolytes (Na2SO4 and H2SO4). The sorption equilibria in the studied system are complex because of three distinct sorption mechanisms: affinity-based interactions, site sharing, and ion exchange. Modelling of the sorption equilibria was attempted using simple sorption isotherms models: the Sheindorf–Rebuhn–Sheintuch (SRS), the Langmuir, and the Sips models. For simplicity, the electrolytes were treated as molecular components (without dissociation). In the case of pure carboxylic acids, both the SRS (residuals 10–5–10–4) and Sips models (residuals ∼ 10–7–10–5) correlated well with the experimental data. However, the Langmuir model was found to be inadequate. In the case of competitive sorption, the SRS model (residuals 10–6–10–4) correlated well with the data, but the Sips model’s (residuals ∼ 10–2) predicted sorption was too strong. Additionally, the sorption of Na2SO4 was well predicted by the SRS model. For each component pair, only a single interaction parameter was required with the SRS model. The sorption equilibria (SRS) model and the column mass balance model were validated against data from batch column experiments done with carboxylic acid-rich feed solutions. Pure water or aqueous carboxylic acid and salt solutions were used as eluents. The model accurately predicted the elution profiles in each case. The characteristic shapes of the carboxylic acid elution profiles with the effects resulting from competitive sorption were well accounted for. Strong sensitivity of the studied system towards changes in pH and H2SO4 concentration was observed.

Biosorption of cationic dyes BY1, BY2 and BG4 by moss Rhytidiadelphus squarrosus from binary solutions

A biosorbent prepared from moss Rhytidiadelphus squarrosus biomass was used for biosorption of cationic dyes – Malachite green (BG4), Auramine O (BY2) and Thioflavine T (BY1) from binary aqueous solutions. Sorption data obtained at non-equilibrium conditions were analyzed by Sheindorf-Rebuhn-Sheintuch (SRS) equation (competitive model for binary systems derived from Freundlich isotherm) and extended model of Freundlich isotherm. Following the comparison of coefficient of determination values (R2) as well as values of root mean squared error (RMSE), the extended model of Freundlich isotherm was more suitable for description of investigated binary systems BG4-BY1 (R2 BG4 = 0.983, R2 BY1 = 0.993) and BG4-BY2 (R2 BG4 = 0.976, R2 BY2 = 0.995). The competition coefficients aij, obtained from SRS model can be considered as a way to quantify mutual competitive interactions. The competition coefficients indicated that the presence of BY1 in binary system decreased the sorption of BG4 (aBY1,BG4 = 0.835) while presence of BG4 (aBG4,BY1 = 0.208) has less pronounced competitive effect on the sorption of BY1 onto biosorbent. Competition coefficients obtained for binary system BY1-BG4 indicate that BG4 (aBG4,BY2 = 0.186) was more significantly affected by the presence of BY2 (aBY2,BG4 = 1.167). Finally, equations used in this work were represented by the three-imensional biosorption isotherm surfaces.

Bioadsorption of nickel and cadmium ions from a binary solution onto sugarcane bagasse lignin: kinetic and thermodynamic study

The single and binary adsorption of Cd(II) and Ni(II) from aqueous solution on lignin of sugarcane bagasse, a secondary product of sugarcane industry, has been demonstrated in this work. Experimental parameters affecting the adsorption are studied, such as the lignin dose, pH, contact time and temperature. The optimal values found for these parameters, both binary and single adsorption, are the followings: lignin dose (7g / L), pH (6), contact time (12 hours) and temperature (40°C). Different empirical adsorption models are used for the evaluation of sorption equilibrium data. Experimental results were interpreted considering speciation curves of ions present in the solution. In single and binary system adsorption data are analyzed using the following adsorption isotherms: single, non-modified, extended and modified Langmuir; single, non-modified and modified Redlich–Peterson; single and extended Freundlich; single and multicomponent Langmuir-Freundlich; and Sheindorf–Rebuhn–Sheintuch. The experimental adsorption isotherms are better adjusted to the extended Langmuir model. This study indicates that the lignin is an adsorbent able to remove Ni (II) and Cd (II) in binary systems, having a greater affinity for cadmium.

Adsorptive interaction of ortho-phenylenediamine with commercial activated carbon in presence of Indole and vice versa: synergistic/antagonistic evaluation

Ortho-phenylenediamine (OPD) and Indole are nitrogenous organic compounds. Ortho-phenylenediamine has been reported to be an endocrine disrupting chemical and is genotoxic in nature, whereas, Indole is mutagenic and carcinogenic. OPD and Indole both all together are present in effluents of several industries, and their simultaneous (binary in the present study) adsorption equilibrium data are required in designing the adsorption system/reactor for separation. Therefore, in the present work, simultaneous adsorption study for adsorption of OPD and Indole from their binary solution, on to low cost commercial grade activated carbon was conducted. Adsorption experiments were performed at 288–318 K, and simultaneous equilibrium adsorption data (binary data in the present study) were collected. Further, various multicomponent competitive isotherms [Langmuir (extended), Freundlich (extended), Sheindorf–Rebuhn–Sheintuch and competitive Redlich–Peterson (modified)] were used to validate the experimental equilibrium isotherm data, and parameters of various isotherms were calculated. Moreover, synergistic/antagonistic effects were also evaluated. Freundlich (extended) and Sheindorf–Rebuhn–Sheintuch isotherm models best represented the experimental data.

Microcystin-LR removal by ion exchange: Investigating multicomponent interactions in natural waters

Microcystin-LR (MCLR) is the most commonly encountered toxic microcystin variant. MCLR is usually present along with common surface water constituents such as inorganic ions and natural organic matter (NOM) which compete with MCLR for active sites during ion exchange (IX) process. Consequently, development of a multicomponent competitive model is essential for practical IX applications. This is critically important given that the NOM characteristics (charge density and molecular weight distribution) and inorganic ions concentrations are spatially variable and can change seasonally. In the present study, a systematic study was carried out into the multicomponent interactions of IX resin with inorganic ions and NOM during the MCLR removal process. This involved evaluation of MCLR removal in a single component system (i.e., MCLR only), a dual component system (MCLR and one other contaminant such as NOM), and a multiple component system (MCLR with NOM and different inorganic ions present in natural waters). A comprehensive understanding of the dynamic adsorption behavior showed that the experimental data for single component systems agree well with a Freundlich isotherm. For multicomponent interactions, the Equivalent Background Concentration (EBC) model which is derived from the Ideal Adsorption Solution Theory (IAST) provided the best correlation with the experimental data in natural waters. The concentrations of competing NOM and inorganic ions estimated by the EBC model were <10% of their initial concentrations. Sulphates are the most competitive inorganic ions followed by nitrates and bicarbonates and the multicomponent interactions could be well predicted by using the IAST-EBC model. However, the EBC model failed in the presence of higher molecular weight Suwannee River Humic Acid (SRHA) molecules due to neglecting of the pore blocking phenomenon. In the presence of higher molecular weight SRHA molecules, the Redlich-Peterson Isotherm (RP) model exhibited a better performance than the Sheindorf–Rebuhn–Sheintuch (SRS) and the EBC models.

Equilibrium Modeling of Ternary Adsorption of Phenols onto Modified Activated Carbon

The prediction of adsorption equilibria in multicomponent systems is of prime importance. Therefore, the equilibrium adsorption data for the following multicomponent systems have been studied. The present paper deals with the simultaneous removal phenol (P), 4-chlorophenol (CP), 4-nitrophenol (NP) and catechol (C), resorcinol (R), hydroquinone (HQ) onto modified activated carbon (MAC) from ternary mixtures. The BET surface area of SC was found to be 934 m2/g, whereas BJH adsorption/desorption surface area of pores is 53.03/58.15 m2/g. The equilibrium adsorption data were obtained at different initial concentrations (C0 = 50–1000 mg/L), 12 h contact time, 30°C temperature, MAC dosage of 10 mg/L at solution pH. Equilibrium isotherms for the ternary adsorption of P–CP–NP and C–R–HQ onto MAC have been analyzed by using non-modified Langmuir, modified Langmuir, extended Langmuir, extended Freundlich and Sheindorf–Rebuhn–Sheintuch (SRS) models. The competitive Sheindorf–Rebuhn–Sheintuch (SRS) model fits for both ternary adsorption equilibrium data satisfactorily and adequately.

Adsorption isotherm models and error analysis for single and binary adsorption of Cd(II) and Zn(II) using leonardite as adsorbent

Leonardite, a by-product from coal mines, was applied to adsorb Cd(II) and Zn(II) from aqueous solutions. Individual and simultaneous adsorptions of the two metal ions were investigated. In a single-component adsorption system, Langmuir and Freundlich isotherms were fitted to the adsorption data. Linear and nonlinear regression methods were used for the assessment of the optimum adsorption isotherm. Error functions including root-mean-square error, sum of the squares of the errors, mean absolute percentage error, Marquardt’s percent standard deviation (MPSD), and Chi-square were applied in the nonlinear regression. The most suitable model for the adsorption of Cd(II) and Zn(II) in the single system is the Freundlich isotherm. The isotherm parameters calculated by MPSD provided the lowest sum of normalized error (SNE) value. The adsorption capacity was found to be 23.89 mg/g for Cd(II) and 16.86 mg/g for Zn(II). It was observed that the adsorption of Cd(II) on leonardite is greater than that of Zn(II). For binary component adsorption systems, Cd(II) and Zn(II) showed antagonistic behavior. The presence of the other metal ions could decrease the amount of metal adsorbed. Binary adsorption of Cd(II) and Zn(II) was tested with regard to four multi-component isotherms: Extended Langmuir, Modified Langmuir, Sheindorf–Rebuhn–Sheintuch, and Extended Freundlich. The Extended Freundlich isotherm proved to be a good fit for the experimental data.

Competitive adsorption isotherm modelling of heterocyclic nitrogenous compounds, pyridine and quinoline, onto granular activated carbon and bagasse fly ash

In the present study, simultaneous adsorption of quinoline and pyridine onto adsorbents such as granular activated carbon (GAC) and bagasse fly ash (BFA) from pyridine–quinoline binary aqueous solution was studied at various temperatures (288–318 K). Gathered equilibrium adsorption data were further analysed using various multicomponent competitive isotherm models such as non-modified and modified competitive Langmuir isotherms, extended-Langmuir isotherm, extended-Freundlich model, Sheindorf–Rebuhn–Sheintuch (SRS) model, and non-modified and modified competitive Redlich–Peterson isotherm model. It was observed that increase in pyridine concentration decreased the total adsorption yield and the individual adsorption yield for both the quinoline and pyridine for both the adsorbents GAC and BFA at all the temperatures studied. Identical trend was observed during the equilibrium uptake of pyridine on to GAC and BFA with an increase in quinoline concentration. The extended-Freundlich model satisfactorily represented the binary adsorption equilibrium data of quinoline and pyridine onto GAC and BFA.

Comparative and competitive adsorptive removal of Ni2 + and Cu2 + from aqueous solution using iron oxide-vermiculite composite

In this study, iron oxide-vermiculite composite (Iovc) with a high specific surface area (SSA) was prepared to remove Ni2+ and Cu2+ from aqueous solution. It was characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared (FTIR), and scanning electron microscopy (SEM). The effects of initial pH of the solution, contact time and adsorbent concentration on the adsorption efficiency were investigated systemically. Equilibrium adsorption isotherms were measured for the single component by using various models. The homogenous adsorption of Ni2+ and Cu2+ was confirmed in the single system by Langmuir and Koble–Corrigan models. For the binary adsorption of Cu2+ and Ni2+ ions have been analyzed by using non-modified Langmuir, modified Langmuir, extended Langmuir, extended Freundlich and Sheindorf–Rebuhn–Sheintuch (SRS) models. The competitive extended Langmuir model described well the competitive adsorption of Ni2+ and Cu2+. Maximum adsorption capacities for Ni2+ and Cu2+ in the binary system are 101.3 and 59.7mg/g, respectively.In the kinetic study, the experimental data fitted well the pseudo-second-order kinetics for Ni2+ and Cu2+ adsorption data. Furthermore, calculated thermodynamic parameters, ΔG°, ΔH° and ΔS° of adsorption showed that the adsorption of Ni2+ and Cu2+ was feasible, spontaneous and an exothermic process.

Competitive adsorption of strontium and cobalt onto tin antimonate

Radioactive strontium (90Sr) and cobalt (60Co) are two major contaminants in low-level radioactive wastewaters from nuclear power plants. In this study, a tin antimonate sorbent (SnSb) used to simultaneously remove Sr and Co was prepared via a new and safe method. The as-prepared SnSb consisted of a composite structure of both pyrochlore and rutile microcrystal dispersed homogeneously at the nanometer scale. The sorbent had a good affinity to both Sr(II) ions and Co(II) ions across a wide pH range of 2–12 or in the presence of various non-radioactive ions. The adsorption competition performance of Sr(II) and Co(II) was investigated, with the adsorption isotherms following the extended Freundlich multicomponent isotherm and Sheindorf–Rebuhn–Sheintuch equation. Although Co(II) was more readily adsorbed on the sorbent, Sr(II) clearly inhibited Co adsorption. The kinetic performance of Sr(II) and Co(II) was described well by a pseudo-second order equation. When compared to the single-component adsorption, the adsorption rate of Sr(II) with Co(II) in the binary-component system decreased due to a competitive adsorption process.

Binary adsorption of heavy metals from aqueous solution onto natural clays

The binary adsorption of Cd(II)–Ni(II) on bentonite, Zn(II)–Cd(II) on sepiolite and Pb(II)–Cu(II) on vermiculite was investigated in this work. The experimental binary adsorption data were interpreted using the following multicomponent adsorption isotherms: non-modified, extended and modified Langmuir; non-modified and modified Redlich–Peterson; extended Freundlich; and Sheindorf–Rebuhn–Sheintuch. The modified Redlich–Peterson multicomponent isotherm best fitted the adsorption data of Cd(II)–Ni(II) on bentonite and Pb(II)–Cu(II) on vermiculite, while the modified Langmuir multicomponent isotherm best fitted the data of Zn(II)–Cd(II) on sepiolite. The competitive adsorption of Cd(II)–Ni(II) on bentonite revealed that both metals presented very similar antagonism toward the adsorption of the other metal. The single metal adsorption on sepiolite showed that the Cd(II) adsorption capacity of sepiolite was 1.3 times greater than that of Zn(II); however, in the binary adsorption, the Zn(II) presented a strong antagonism to the adsorption of Cd(II), but Cd(II) did not affected the adsorption of Zn(II). The single adsorption isotherms of Cu(II) and Pb(II) on vermiculite revealed that the affinity of the vermiculite towards Pb(II) was slightly higher than that of the Cu(II). However, in the competitive adsorption, the affinity of Pb(II) towards the vermiculite was much higher than that of the Cu(II).

Influence of humic acids on the adsorption of Basic Yellow 28 dye onto an iron organo–inorgano pillared clay and two Hydrous Ferric Oxides

Effect of humic acids (HAs), macromolecules from natural organic matter, on the adsorption of Basic Yellow 28 is the aim of the present work. Three adsorbents were investigated in this study: an iron organo–inorgano pillared clay and two synthetic Hydrous Iron Oxide (Goethite and HFO). The surface charge was positive in the pH range of this study for the pillared clay; in contrast, it changes from positive to negative when the pH value increased (pH>9) for the two (oxy)hydroxides. Pseudo-first order kinetic rate constants and adsorption capacities increase from humic acid to BY 28. Adsorption isotherms of BY 28 and HA in single component were analysed using the Freundlich equation. Adsorption capacities increased sharply when the pH value of the dye solution was raised from 3 to 9. Increasing the pH medium from 3 to 9 reduces the HA adsorption capacities onto Fe-SMPM and iron oxyhydroxides, respectively. Fitting between measured and predicted sorption capacities of BY 28 and HA in a binary component system indicates that the Sheindorf–Rebuhn–Sheintuch (SRS) model, an extended Freundlich model, is able to describe the simultaneous adsorption of BY 28 and HA. Humic acids favourably affect the adsorption of BY 28, and a cooperative mechanism could be suggested. The synergetic effect existing between BY 28 and HA is shown by the interaction coefficients η12, which are generally high and increase with pH. Some phenomena have been advanced to explain this mechanism.

Adsorption of basic dyes in single and mixture systems on granular inorganic–organic pillared clays

The adsorption of two basic dyes, CI Basic Yellow 28 and CI Basic Green 4, was studied in single and binary solute systems using two classes of inorganic–organic pillared clay granules as sorbents (300–400 µm and 700–800 µm). These were prepared by high‐shear wet granulation from an Al cetyltrimethylammonium bromide intercalated clay powder (particle diameter < 50 µm). Adsorption rate data indicate that BY 28 adsorbs more rapidly than BG 4 and a pseudo‐first‐order model was found to fit the kinetic curves, with regression coefficients above 0.98. Adsorption isotherms in single solute systems at pH 3 and pH6 were respectively analysed according to the Langmuir and Freundlich models using non‐linear regression. Best fits were obtained with the Langmuir model. In binary dye systems the adsorption at three molar ratios (1:9, 1:1 and 9:1) demonstrated that the adsorption of BG 4 was greater than that of BY 28 on all the sorbents studied; this was in agreement with the results obtained for single solute systems. Increasing the granule size decreased dye adsorption, an effect in accordance with the Sheindorf–Rebuhn–Sheintuch model.

Adsorption equilibria between dye and surfactant in single and binary systems onto geological materials

Abstract Adsorption characteristics of cationic dyes and surfactants onto clay and sandstone from a single component system were studied using toluidine blue (TB) and cetyl trimethylammonium bromide (CTAB). Equilibrium data of TB and CTAB in the single solute systems fit well to the Langmuir and the Freundlich adsorption isotherms. Competitive adsorption was observed between dye and surfactant cations. The effect of sodium chloride on dye and surfactant adsorption was studied in TB–NaCl and CTAB–NaCl binary systems. Equilibrium adsorption for binary systems was analyzed by using the extended Langmuir and the extended Freundlich models. Adsorption results for the TB–CTAB system onto both adsorbents were also well described by the Sheindorf–Rebuhn–Sheintuch (SRS) model for multi-component systems. Free energy changes for adsorption systems were calculated using thermodynamic equilibrium constants evaluated from selectivity coefficients of the binary systems. The site distribution functions estimated using Freundlich model parameters gave valuable information about the ratio of the adsorption sites on adsorbent surface having different affinity for competing cations.

Equilibrium Modeling of Ternary Adsorption of Metal Ions onto Rice Husk Ash

The aim of the present study is to analyze the competitive adsorption of cadmium (Cd(II)), nickel (Ni(II)), and zinc (Zn(II)) ions onto rice husk ash (RHA) from ternary metal ion mixtures. RHA is a waste material obtained from the flue gas of the rice husk fired boilers. The equilibrium adsorption data were obtained at different initial concentrations (C0 = 10 to 100 mg·dm−3), 5 h contact time, 30 °C temperature, and RHA dosage of 10 mg·dm−3 at pH = 6. The Freundlich and the Redlich−Peterson models represent the single ion equilibrium adsorption data better than the Langmuir model. The equilibrium metal removal decreases with increasing concentrations of the other metal ions, and the combined action of Cd(II), Ni(II), and Zn(II) ions on RHA is found to be antagonistic. The competitive Sheindorf−Rebuhn−Sheintuch (SRS) model fits the ternary adsorption equilibrium data satisfactorily.

Adsorptive Removal of Acid Blue 113 and Tartrazine by Fly Ash from Single and Binary Dye Solutions

Adsorption of two acid dyestuffs, acid blue 113 (AB) and tartrazine (TA), has been studied from their single and binary solutions by using fly ash (FA) as an adsorbent. The S shaped isotherms observed for dye adsorption from single solutions show that both acid dyes are not preferred at a low concentration region whereas adsorption of the dyes from binary solutions is enhanced via solute-solute interactions. Although the L-shaped isotherm is observed in binary solutions adsorbability of AB decreases in concentrated solutions with respect to single one, time dependency of adsorption is well described with a pseudo-second-order kinetic model as well as the linear relation of Bt vs. t plots (not passing through origin) indicates that film diffusion is effective on dye adsorption. Modeled isotherm curves using isotherm parameters of the Freundlich and Dubinin-Radushkevich (D-R) equations adequately fit to experimental equilibrium data. Equilibrium adsorption of AB in binary solutions has been quite well predicted by the extended Freundlich and the Sheindorf-Rebuhn-Sheintuch (SRS) models. In general, the isotherm curves constructed in the temperature range of 298–328 K show that the optimum temperature is 318 K for AB removal from both single and binary solutions.

Removal of cadmium(II) and zinc(II) metal ions from binary aqueous solution by rice husk ash

The present study reports the competitive adsorptive removal of cadmium (Cd(II)) and zinc (Zn(II)) ions from binary systems using rice husk ash (RHA), a waste obtained from the rice husk-fired furnaces, as an adsorbent. The initial pH (pH 0) affects significantly the capacity of RHA for adsorbing the metallic ions in the aqueous solution. The pH 0 ≈ 6.0 is found to be the optimum for the removal of Cd(II) and Zn(II) ions by RHA. The single ion equilibrium adsorption from the binary solution is better represented by the non-competitive Redlich–Peterson (R–P) and the Freundlich models than by Langmuir model in the initial metal concentration range of 10–100 mg/l. The adsorption of Zn(II) ion is more than that of Cd(II) ion, and this trend is in agreement with the single-component adsorption data. The equilibrium metal removal decreases with increasing concentrations of the other metal ion and the combined effect of Cd(II) and Zn(II) ions on RHA is generally found to be antagonistic. Non-modified Langmuir, modified Langmuir, extended-Langmuir, extended-Freundlich, Sheindorf–Rebuhn–Sheintuch (SRS), non-modified R–P and modified R–P adsorption models were tested to find the most appropriate competitive adsorption isotherm for the binary adsorption of Cd(II) and Zn(II) ions onto RHA by minimizing the Marquardt's percent standard deviation (MPSD) error function. The extended-Freundlich model satisfactorily represents the adsorption equilibrium data of Cd(II) and Zn(II) ions onto RHA.

Modelling Individual and Competitive Adsorption of Cadmium(II) and Zinc(II) Metal Ions from Aqueous Solution onto Bagasse Fly Ash

The present study deals with the competitive adsorption of cadmium (Cd(II)) and zinc (Zn(II)) ions onto bagasse fly ash (BFA) from binary systems. BFA is a waste obtained from the bagasse‐fired boilers of sugar mills. The initial pH≈6.0 is found to be the optimum for the individual removal of Cd(II) and Zn(II) ions by BFA. The equilibrium adsorption data were obtained at different initial concentrations (C 0 = 10–100 mg/l), 5 h contact time, 30°C temperature, BFA dosage of 10 mg/l at pH 0 = 6. The Redlich–Peterson (R–P) and the Freundlich models represent the single ion equilibrium adsorption data better than the Langmuir model. The adsorption capacities in the binary‐metal mixtures are in the order Zn(II)>Cd(II) and is in agreement with the single‐component adsorption data. The equilibrium metal removal decreases with increasing concentrations of the other metal ion and the combined action of Cd(II) and Zn(II) ions on BFA is found to be antagonistic. Equilibrium isotherms for the binary adsorption of Cd(II) and Zn(II) ions on BFA have been analyzed by non‐modified Langmuir, modified Langmuir, extended‐Langmuir, Sheindorf–Rebuhn–Sheintuch (SRS), non‐modified R–P and modified R–P adsorption models. The isotherm model fitting has been done by minimizing the Marquardt's percent standard deviation (MPSD) error function using MS Excel. The SRS model satisfactory fits for most of the adsorption equilibrium data of Cd(II) and Zn(II) ions onto BFA.

Competitive adsorption of phenols on organically modified layered hexaniobate K 4Nb 6O 17

Layered hexaniobate K 4Nb 6O 17 was intercalated with two cationic surfactants, dodecylammonium (C 12N) and dioctadecyldimethylammonium (2C 182MeN) ions, and the obtained intercalation compounds were utilized as adsorbents for phenols dissolved in water. Competitive adsorption of phenol, 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP), in binary- and ternary-solute systems was investigated. Both the adsorbents showed high adsorption selectivity for 2,4-DCP. The uptake of each solute was reduced by the presence of the other species, and the reduction in the multi-solute systems depended on the hydrophobicity of the adsorbates coexisted in the solution. For the adsorbent modified with 2C 182MeN, however, uptakes of the solutes were enhanced by the presence of each other at low equilibrium concentrations in comparison with the single-solute solutions, because of cooperative adsorption. Adsorption isotherms of phenols in single-solute systems plotted against the equilibrium concentrations normalized with the solubility in water suggested that solute portioning was the main adsorption mechanism. Freundlich adsorption model succeeded in fitting the adsorption isotherms of phenols on the niobate modified with C 12N cations in single-solute systems, and prediction of the competitive adsorption behavior of phenols with the Freundlich-based Sheindorf–Rebuhn–Sheintuch (SRS) model gave acceptable results.